Iodine is a very important trace element necessary in the biosynthesis of thyroid hormones. Iodine is required for developing and maintaining healthy body. There are well known Iodine Deficiency Disorders like Goiter and Cretinism. The edible salt is chosen as a vehicle in the provision of iodine because of its uniform consumption and availability to all segments of population independent of social or economic status. During the past twenty years, there has been a strong effort, lead by the United Nations, to iodize all salt for human consumption. Potassium iodate and potassium iodide are most often used in iodizing the edible salt. The Food and Nutrition Board of National Research Council of the USA placed the optimum requirement of iodine at 150-300 μg per day, and considering 10 gm of salt consumption per day, the iodisation level of salt could be around 15-30 mg per kg of salt. The impurities present in edible salt, moisture and temperature are some of the main factors that induce loss of iodine from iodized salt. In order to deliver adequate amount of iodine to the consumer while avoiding the unnecessary excess addition of iodizing agent in salt that is normally done to compensate for losses, it is of paramount importance that an ultrastable iodizing agent should be developed. This would allow a simultaneous benefit in as much as it may not be necessary to purify salt excessively as is the practice at present to minimize iodine loss apart from imparting a superior aesthetic effect such as free flow nature. The latter is especially important, as it is well known that impurities such as magnesium are required as micronutrient and can also enhance the saltiness of salt.
Reference may be made to a paper entitled “Stability of iodine in iodized salt” by L. L. Diosady and Venkatesh Mannar, published in The Proceedings of 8th World Salt Symposium, 2000, Volume 2, pp 977-982, wherein it is stated in the abstract that, “since iodine readily sublimes at ambient temperature, the effectiveness of salt iodisation programs depends on the stability of the iodine carrier, typically potassium iodate.” The authors further state that they examined the stability of iodine in typical salts available in 12 countries in a controlled laboratory setting, at 40° C. and controlled humidity (60 or 100%) for periods up to 12 months. Iodine was rapidly lost in most unrefined salt samples. Further, the presence of moisture due to hygroscopic impurities, and metal ion impurities, such as iron accelerated the loss of iodine.
Reference may be made to a paper entitled “Stability of iodized salt with respect to iodine content” by S. A. Chauhan et al. in Research and industry, March 1992, Vol 37, pp 38-41 wherein stability of iodine in iodized salt prepared by submersion method using solution of potassium iodate was studied for iodized salt packed in HDPE bags, for iodized salt exposed to atmosphere, iodized salt solution on boiling and iodized salt under heating up to 120° C. The draw back associated with this work evinces that there is considerable loss of iodine during storage in bags or in open atmosphere. Moreover, significant loss of iodine is observed on boiling the salt solution or heating the iodised salt.
Reference may be made to a paper entitled “The stability of potassium iodate in crude table salt”, by Arroyave, G. et. al., in Bull. World Health Organisation, 1956, 14, pp 183-155, wherein potassium iodate was stabilized by calcium carbonate in crude sea salt stored in hemp fiber sacks for up to eight months at ambient temperatures and relative humidity between 70 and 84%. Only some 3.5% of added iodine was reported to be lost. The main draw back is that the stability of iodine under exposure to atmosphere and under variable temperature has not been studied. However, as is well known to practitioners in this field, this is not the approach followed in practice for stabilization, presumably because the results are not as encouraging as that indicated in the above report.
Reference may be made to a paper entitled “Micro encapsulation for iodine stability in salt fortified with ferrous fumarate and potassium iodide” by Diosady L. L. et. al., in Food Research International, 2002, Volume 35, Issue 7, pp 635-642 wherein potassium iodide and potassium iodate were encapsulated in modified starches, gelatin, sodium hexametaphosphate and purified sodium chloride by spray drying and fluidized bed drying to produce microcapsules containing 0.3 to 2% iodine. The most stable combination, containing 50 mg iodine and 1000 mg iron per kg salt, retained more than 75% of the added iodine for a year at 40° C., 100% RH. The authors have not given data on stability of iodine for singly fortified salt but even if it were very stable, the process of micro encapsulation is expensive.
Reference may be made to the paper entitled “Synthesis, thermal investigations and solubility of a new double salt K2Mg(IO3)4.2H2O” by D. Rabadjieva and M. Maneva in Thermochimica Acta, 1997, Vol 293, pp 117-123, which describe the thermal properties of the new IO3-containing double salt. There is no mention of its suitability, if any, as an iodizing agent. Moreover, the high local concentration of iodine would make it difficult to guarantee uniform distribution in the product while ensuring a total iodine not exceeding 30 ppm.
Reference may be made to the paper entitled “The properties of salt-filled sodalites. Part 4. Synthesis and heterogeneous reactions of iodate-enclathrated sodalite.” By Joseph Christian Buhl, in “Thermochimica Acta, 1996, Vol 286, pp 251-262, where in sodalite solid solution Na8[AlSiO4]6(IO3)2-x(OH.H2O)x; (0.7<x<1.3) is produced from the system Na2O—2SiO2—Al2O3—NaIO3—H2O under hydrothermal conditions. The main disadvantage of this kind of compound for its use as iodising agent in the preparation of iodised salt is its high alkalinity that would make it unsuitable in pharmaceutical or food application. Further, the concentration of iodate in this compound is too high for even distribution in edible salt.
Reference may be made to the paper entitled “Anionic clay minerals” by W. T. Reichle, in Chemtech, January 1986, pp 58-63 which describes the structure and properties of hydrotalcites which are layered anionic clays bearing the chemical composition [Mg6Al2(OH)16CO3.4H2O]. These materials are used widely in antacid formulations as well as other applications such as halogen scavenger, adsorbent for wastewater treatment, stabilizer in poly-vinyl chloride and fire-retardant. There is no report however of the use of such materials for the preparation of iodizing agent.
Reference may be made to the paper entitled “Adsorption behavior of IO3− by CO32− and NO32−—hydrotalcite” by Takashi Toraishi et. al. in Applied Clay Science, 2002, 22, pp 17-23, wherein the adsorption behavior of iodate by hydrotalcite type compounds with CO3 (HTCO3) and NO3 (HTNO3) was studied for their application in removal of iodate from radioactive waste for disposal. The authors found that HTNO3 can adsorb iodate but no mention is made of the possible use of such methodology for preparation of iodizing agent. Moreover, HTNO3 is not recommended for edible purpose.
Reference may be made to P.M.Oza et. al. in Indian patent application No. 1053/DEL/2000, where in an improved process for the preparation of Hydrotalcite from bittern-mother liquor left after separation of salt has been disclosed. The hydrotalcite contains carbonate anion and no attempt was made to substitute the carbonate with other anions.
Reference may be made to the paper entitled “The use of Hydrotalcite as an anion adsorbent” by Linda M. Parker et. al. in Ind. Eng. Chem. Res. 1995, 34, pp 1196-1202 where in use of fired and non fired HTCO3 for adsorption of anions like Cl−, Br−, NO3−, HPO4−, SO4− and borate was studied carried out. However, there is no mention of any study with iodate anion.